Frequency counter circuit



NOV. 26, 1946. P. F. G. HoLsT ETAL FREQUENCY COUNTER CIRCUIT Filed N'ov.so, 1944 wm. w

Patented Nov. 26, 1946 FREQUENCY COUNTER CIRCUIT Paul F. G. Holst andLoren R. Kirkwood; Oaklyn, N. J., assignors to Radio Corporation ofAmerica, a corporation of Delaware Application November 30, 1944, SerialNo. 565,973

8 Claims.

The invention covered herein may be manufactured and used by or for theGovernment of the United', States for any governmental purpose withoutpayment to us or assigns of any royalty thereon.

Our invention relates to frequency counter or frequency divider circuitsof the type wherein pulses of current are applied through a diode or thelike to a storage capacitor so that the voltage across the capacitorchanges in steps.

An object of the present invention is to provide an improved countercircuit that is operated by voltage pulses comprising a positive voltageswing followed by a negative voltage swing.

A further object of the invention is to provide an improved frequencycounter or divider circuit that is not affected by the negative part ofthe voltage pulses.

A further object of the invention is to provide an improved frequencycounter or divider circuit in which each incoming pulse produces onlyone well defined step in the voltage across the storage capacitor.

A still further object of provide an improved counter circuit that isalways properly reset or returned to its original condition by itstriggering of the blocking oscillator included in the counter circuit.

In a preferred embodiment of the invention the input or chargingcapacitor of the counter is provided with a resistor leak in place ofthe diode commonly used for discharging it at the end of an appliedpositive pulse. A diode is connected between the input capacitor and thestorage capacitor so that current pulses flow into the storage capacitoronly in response to applied positive pulses. Each applied positive pulseraises the storage capacitor potential one step until it is high enoughto trigger the blocking oscillator. Each time said blocking oscillatoris triggered, the storage capacitor is discharged by the grid current ofthe blocking oscillator tube. Preferably, a diode is connected acrossthe storage capacitor with such a polarity that it will discharge thestorage capacitor when the blocking oscillator has driven the voltageacross it below ground potential.

Other objects, features and advantages of the invention will be apparentfrom the following description taken in connection with the accompanyingdrawing in which `Figure l is a circuit diagram of one preferredembodiment of the invention and Figures 12 and 3 are graphs that arereferred to in explaining the operation of the circuit shown in Fig. l.

the invention is to Fig. 1 shows a frequency counter enclosed within therectangle I0 embodying the present invention. The counter I0 in theexample shown has pulses II applied to it from a blocking oscillator I2that produces pulses having the positive p0rtions I Ib and preceding thenegative portions I Ia (Figs. 1 and 3). For the purpose of illustration,it is assumed that the blocking oscillator I2 is part of a. conventionalcounter circuit that has a counter storage capacitor I5 included in theoscillator grid circuit.

Our improved counter circuit I0 comprises a diode I3 having an anode I4and a cathode IB, a diode II having an anode I8 and a cathode I9, aninput or charging capacitor 2|, and a storage capacitor 22. The diode I3is connected in series with the capacitors 2| and 22 in the polarityrequired for the positive pulses IIb to apply a charge to the capacitor22. As in customary counter Circuit design, the charging capacitor 2l isof small capacity compared with that of the storage capacitor 22.

After the positive part IIb of each pulse I I occurs, the resultingcharge on the capacitor 2I is removed by a leak resistor 20 which isconnected from the diode side of capacitor 2I to ground. In the usualcounter circuit the function of the leak resistor 20 is performed by adischarge diode whose anode is connected to ground and whose cathode isconnected to the anode of diode i3. The advantage in the use of a leakresistor 2u of the correct value will be explained hereinafter.

The oscillator portion of the counter circuit i0 is preferably ablocking oscillator 25 that comprises a triode tube 23 having a cathode29, a grid 3I and an anode 32. A transformer 33 having a primary 34 anda secondary 3B is provided to couple the plate circuit to the cathodecircuit. The lov/potential end of the secondary 3E is bypassed to groundthrough a lter capacitor 3?; also it is connected through a variable tap21 to a positive bias voltage on a potentiometer resistor 35. The highpotential end of the secondary 36 is coupled to the cathode 29 through arelatively small resistor 43 (of 33 ohms resistance, for example) whosefunction will be discussed more fully later in this description.

The grid 3l of the blocking oscillator tube 28 is connected through aconductor 38 to one side of the storage capacitor 22. v Thus, when thisside of the capacitor 22 becomes sufficiently positive with respect toground, the tube 28 Will commence to conduct a current and the resultingoscillation will produce a pulse. It will be under- StOod that the tube28 is normally blocked by the agitare positive bias potential applied tothe cathode 25 from the tap 2l on the potentiometer 35.

The diode I I is connected across the storage capacitor 22 in thepolarity required to discharge capacitor 22 in the event that it ischarged to a negative potential with respect to ground when theoscillator 25 is triggered and goes through an oscillation. It may benoted that in counter circuits using a discharge diode in place of thedischarge or leak ,resistor 20, the function of the diode I1 isperformed by the discharge diode and the diode I3 in series.

The operation of the counter is as follows: The blocking oscillator 25normally is blocked by the positive bias from the tap 21 on the resistor35. That is, the oscillator tube 28 is biased beyond anode currentcut-oi by the positive voltage on its cathode 29.

Now when a series of positive pulses II b is applied to the counterthrough the charging capacitor 2l, the current pulse ow through thediode I3 into the capacitor 22 is in the direction to charge the storagecapacitor 22 positive step by step with respect to ground potential.Each positive pulse IIb results in a current pulse and since the leakresistance 20 is high compared to the resistance of the diode I 3, theeffect of the leak resistance during the pulse period may be neglected.Under the above assumption, all current flowing to the storage capacitor22 is obtained from the input capacitor 2l, and both condensers willtherefore become charged. Since the storage capacitor 22 has a fargreater value than the input capacitor 2|, the greatest voltage changewill occur on the input capacitor 2l. The total change in voltage acrossthe two capacitors will equal the positive peak of the pulse. After thepulse II has reached its maximum positive voltage, and both oondensersare fully charged, the current through the diode I3 will stop. Thecharge thus placed on the storage capacitor 22 cannot be conductedthrough the diodes I3 and Il, since this would require the diodes toconduct a current from their cathodes to their anodes. The storagecapacitor 22 will therefore remain charged. On the other hand, thecharge placed on the input capacitor will leak oi` through the resistor2li. 'Ihe resistance value of the leak resistor 20 is made such that thecharging condenser 2I will discharge during the time interval betweensuccessive applied pulses IIb, which interval is long compared with theduration of a pulse IIb.

The above described action produces across capacitor 22 the steppedvoltage wave di (Figs. 1

and 2). The tap 21 is adjusted so that a predetermined number of pulsesIIb will increase the voltage 4I to a value where the oscillator tube 28begins to draw anode current. As a result, the oscillator 25 goesthrough one oscillation to produce the pulse 4211-4211, and thecapacitor 22 is discharged by the grid current of the oscillator tube 28during the time the oscillator grid is positive.

While it is desired to operate the blocking os cillator 25 with such anamplitude that a full discharge of the storage capacitor 22 is assured,it is not advisable to operate the oscillator at a much higher levelon'account of the large pulse currents which exist. If the resistor 43is omitted, the pulse amplitude will be greatly in excess of therequired amplitude. Resistor 43 is therefore added to limit the tubecurrents without injuring the performance of the counter circuit.

It will be apparent that by employing the leak .conducting deviceconnected resistor 2li in place of the usual discharge diode, each pulsewill produce one well defined step in the voltage across the 4storagecapacitor 22. Using a discharge diode, the charge on the input capacitor2| will change during the voltage swing which follows the positive peakso that when the voltage swings in the positive direction. after themaximum negative voltage another charge will be placed on the storagecapacitor 22. Thus each pulse will place two charges on the storagecapacitor 22, resulting in two steps instead of one well defined step.By employing our invention, this difficulty is avoided.

` We claim as our invention:

1. In combination, a charging capacitor of comparativelyl smallcapacity, av unidirectional conducting device and a storage capacitor ofcomparatively large capacity connected in series in the order named,means for impressing a pulsating voltage across said series circuit,thereby causing said pulses to place charges on both capacitors, and aleakage resistor connected between the junction of the. chargingcapacitor and said conducting device and the free plate of said storagecapacitor, thereby substantially discharging the charging capacitorduring the period between successive applied pulses.

2. In combination, a storage capacitor, a charging capacitor, aunilaterally conducting device connected between one plate of each ofsaid capacitors for admitting current from said charging capacitor tosaid storage capacitor to charge it in a certain polarity, a leakageresistor connected between the junction of the charging capacitor andsaid conducting device and the other plate oi` said storage capacitorfor discharging said charging capaciton means for lmpressing a pulsatingcurrent between said other plate of the storage capacitor and the otherplate of the charging capacitor, a second unilateral across said storagecapacitor in the polarity required to discharge said storage capacitorif it starts to acquire a charge in a polarity opposite to said certainpolarity, and a loading impedance across the storage capacitor fordischarging the storage capacitor following a predetermined charge ofsaid certain polarity thereon.

3. In combination, a storage capacitor, a charging capacitor, aunilaterally conducting device connected between one plate of each ofsaid capacitors for admitting current from said charging capacitor tosaid storage capacitor to charge it in a certain polarity, a, leakageresistor connected between the junction of the charging capacitor andsaid conducting device and the other plate of said storage capacitor fordischarging said charging capacitor, means for impressing periodicelectrical pulses between said other plate of the storage capacitor andthe other plate of the charging capacitor, a second unilateralconducting device connected across said storage capacitor in thepolarity required to discharge said storage capacitor if it starts toacquire a, charge in a polarity opposite to said certain polarity, andmeans comprising an oscillator connected across the storage capacitorfor producing an electrical pulse and for discharging the storagecapacitor in response to a predetermined charge `of said certainpolarity thereon.

4. In combination, a storage capacitor, a, charging capacitor, aunilaterally conducting device connected between one plate of each ofsaid capacitors for admitting current from said charging capacitor tosaid storage capacitor to charge yblocking oscillator for impressingperiodic electrical pulses between said other plate of the storagecapacitor and the other plate of the charging capacitor, said periodicpulsesl having `positive and negative portions, a second unilateralconducting device connected across said storage capacitor in thepolarity required to discharge said storage capacitor if it starts toacquire a charge in a polarity opposite to said cer.- tain polarity, andmeans comprising an oscillator connected across the storage capacitorfor producing an electrical pulse and for discharging the storagecapacitor in response to a predetery mined charge of said certainpolarity thereon.

5,. A frequency counter comprising a charging capacitor, a unilateralconducting deviceand a storage capacitor connected' in series with eachother, said device being connected in the polarity required for an inputpulse of a certain polarity to cause current ilow into said storagecapacitor to charge it at said certain polarity when it is applied tosaid charging capacitor, a leak resistor connected between ground andthe junction point of said charging capacitor and said unilateralconducting device, said leak resistor having a resistance value such astol discharge said charging capacitor at the end of each applied pulse,and an oscillator comprising a vacuum tube having an electrode connectedto the high potential side of said storage capacitor, said oscillator being normally blocked and being adjusted to oscillate to produce a pulsein response to said storage capacitor being charged to a predeterminedpotential oi said certain polarity, and a second unilateralv conductingdevice connected across said storage capacitor in the polarity requiredto discharge said storage capacitor in the event` that it starts tochargent a polarity opposite to said certain polarity. l

6. A frequency counter comprising a charging capacitor, a unilateralconducting device and a storage capacitor connected in series with eachother, said device being connected in the'polarity required for apositive input pulse to cause current flow 'into said storage capacitorwhen it is applied 'to said charging capacitor, la leak resistorconnected between ground and the junction point o! said chargingcapacitor and said unilateral conducting device, said leak resistorhaving a resistance value such as to discharge said charging capacitorat the end `of each applied positive pulse, and an oscillator comprisinga vacuum tube having a grid connected to the y high potential side ofsaid storage capacitor, said oscillator being normally blocked and beingadjusted to oscillate to produce a pulse in response to said'storagecapacitor being charged to a predetermined positive potential, and asecond unilateral conducting device connected across said storagecapacitor in the polarity required to. discharge said storage capacitorin the event that it starts to charge negatively with respect `toground.

l7. In combination, a blocking oscillator comprising a vacuum tubehaving an anode, a control grid and a cathode, a storage capacitor towhich said grid is connected, a charging capacitor and a unilateralconducting device connected in series with each other and said storagecapacitor, said unilateral conducting device being connected in thepolarity required to produce a positive charge on said storage capacitorin response to the application of a positive input pulse to saidcharging capacitor, and a second unilateral conducting device connectedacross said storage capacitor in the polarity required to prevent saidstorage capacitor from acquiring a negative charge, and a leak resistorconnected between ground and the junction point of said chargingcapacitor and said unilateral conducting device to discharge saidcharging capacitor at the end of each positive input pulse.

8. A frequency counter comprising a charging capacitor, a. unilateralconducting device and a storage capacitor connected in series with eachother, said device being connected in the polarity required for apositive input pulse tccause current flow into said storage capacitorwhen itis applied to said charging capacitor, a leak re' sistorconnected between ground and the :lunction point of said chargingcapacitor and said unilateral conducting device, said leak resistorhaving a resistance value such as to discharge said charging capacitorat the end of each applied positive pulse, and a blocking oscillatorcomprising a vacuum tube having a. grid connected to the high potentialside or said storage capacitor and having input and output circuitscoupled through a transformer having a primary and a secondary, one endof said secondary being connected to the cathode of said tube, and theother end of said secondary being connected to a point of positive bias,and a second unilateral conducting device connected across said storagecapacitor in the polarity required to discharge said storage capacitorin the event that it starts to charge negatively with respect to ground.

c- PAUL F. G. HOLBT.

IDEEN R. KIRKWOOD.

